Add organizing files into Artist/Album/01 Title from their tags

A new Organize tab renames audio files from their tags into a per-pair
naming pattern, by default {artist}/{album}/{track} {title} (album
artist, falling back to artist). Multi-disc albums get a disc prefix
(2-04) or a Disc N folder; names are made safe for Windows/SMB shares.

- Preview first: every rename, files already organized, and files
  skipped with the reason (missing tags, with a button into the tag
  editor; two files resolving to the same name; an existing file).
- Applying re-checks each file against the preview, moves it within its
  library (hardlinks and contents untouched, case-only renames via a
  temporary name, completed on startup after a crash), carries .lrc
  lyrics and folder cover art along, and removes emptied folders. Each
  move is an operation that can be undone; the library is rescanned.
- Optional automatic organizing of the slave, master or both during
  scans (off by default). Dry run applies.
- Scans now recognise a slave file that is a hardlink of a master file
  at a different path as linked ("same file, other path") instead of
  unmatched.

Migration 7 adds the per-pair naming settings.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/engine/ops.go

@@ -625,6 +625,17 @@ func (e *Engine) Undo(ctx context.Context, opID int64) error {
 	if err != nil {
 		return err
 	}
+	if o.Action == store.ActMove {
+		if err := undoMove(l, o); err != nil {
+			return err
+		}
+		if err := e.st.MarkUndone(ctx, o.ID); err != nil {
+			return err
+		}
+		e.log.Info("file move undone", "op", o.ID)
+		_, _ = e.StartScan(o.PairID, "undo")
+		return nil
+	}
 	if o.Action == store.ActTags {
 		if err := e.undoTags(ctx, l, o); err != nil {
 			return err
@@ -858,6 +869,13 @@ func (e *Engine) Recover(ctx context.Context) {
 		return
 	}
 	for _, o := range ops {
+		if o.Action == store.ActMove {
+			if l, err := e.loadPair(ctx, o.PairID); err == nil {
+				recoverMove(l, o)
+			}
+			_ = e.st.FinishOp(ctx, o.ID, store.OpInterrupted, "interrupted by shutdown; rescan to verify state")
+			continue
+		}
 		if o.Action == store.ActTags {
 			msg := e.recoverTags(ctx, o)
 			_ = e.st.FinishOp(ctx, o.ID, store.OpInterrupted, msg)